Driven by the ever-increasing demand for chiral chemicals, the development of new and efficient methods to provide enantioenriched products is of great interest to both academia and industry. Catalytic asymmetric reactions using organocatalysts provide one of the most powerful and economical synthetic approaches to a variety of enantiomerically enriched compounds. The development of new privileged chiral ligands and catalysts that exhibit high reactivity and enantioselectivity is always a challenging endeavour for an organic chemist. State-of-the-art chiral ligands generally come from the profound understanding of catalytic process, the creativity of organic chemists and sometimes, a degree of serendipity. The most important feature of privileged chiral catalysts is the highly rigid structures, with multiple oxygen-, nitrogen-, or phosphorous-containing functional groups to bind strongly to reactive metal centers [e.g. Yoon, T P, & Jacobsen, E N, Science (2003) 299, 1691-1693 or Pfaltz, A, & Drury III, W J, PNAS (2004) 101, 5723-5726]. Another important point is that it should be easily prepared and modified, thus fit well to a combinatorial approach for finding the most suitable ligand for a particular catalytic asymmetric transformation. A compound that has been ascribed as a “universal catalyst” due to its widespread application in organocatalysis is proline. However, it is widely accepted that proline is usually not an efficient catalyst in terms of yield and enantioselectivity for electrophiles that are poor hydrogen bond acceptors such as nitroalkenes.
Unfortunately, with most organocatalysts for asymmetric catalysis the use of high catalytic loading (>10 mol %), the need to use anhydrous organic solvents or/and the narrow substrate scope limit their applicability to complex molecule synthesis. Furthermore, the organocatalyzed functionalization of biomolecules in water remains a challenge.
Therefore, there remains a need for novel organocatalysts. It would also be particularly useful to provide an organocatalyst which can work nicely in both water and organic solvents.